In order to mix a plurality of fluids together in-line, there has heretofore been employed a method by making use of a Venturi tube which, as shown in FIG. 13, has a narrowing channel forming a contracting portion 104, a throat portion 105 and a flaring portion 106 in a continuing manner. In FIG. 13, a primary fluid flows in through an inlet channel 101, passes through the contracting portion 104, throat portion 105 and flaring portion 106 in this order, and flows into an outlet channel 103. In this case, the throat portion 105 is designed to have a sectional area smaller than the sectional areas of the inlet channel 101 and the outlet channel 103. Therefore, the fluid flows through the throat portion 105 at an increased velocity, producing a negative pressure in the throat portion 105. As a result, a secondary fluid is sucked from a suction channel 102 communicated with the vicinity of the throat portion 105 due to the negative pressure, mixed into the primary fluid and flows out through the outlet channel 103. Thus, such an in-line-type fluid mixer has an advantage in that no special device such as a pump is necessary for injecting the secondary fluid.
In the above fluid mixer, however, the fluid to be sucked joins the flow from a direction deviated in the circumferential direction from the suction channel 102 communicated with the inner circumference of the throat portion 105. Therefore, the fluids tend to be inhomogeneously mixed together in the channel. In order to avoid inhomogeneous mixing and to more homogeneously mix and stir the fluids, it is necessary to install a stationary mixer or the like in the downstream of the in-line fluid mixer.
To solve the above problem, a liquid mixer using a jet nozzle as shown in FIG. 14 has been proposed (see JP 2009-154049 A). In this liquid mixer, a raw water passage 107 is provided with an ejector 109 for ejecting a chemical solution fed from a chemical solution introduction pump 108 and a mixer 110 in the downstream of the ejector 109. Further, in the immediate downstream of a nozzle member 111 of the ejector 109, there is a negative pressure-generating space 113 having a sectional area larger than that of a jet 112 of the nozzle member 111. The raw water is introduced from the raw water passage 107 into an inner passage 114 of the nozzle member 111 and is injected from the jet 112, whereby a negative pressure is generated in the negative pressure-generating space 113 and the chemical solution is introduced from an introduction communication passage 115.
By using the above ejector 109, the chemical solution flowing in from the introduction communication passage 115 is mixed into the raw water from the entire circumferential directions along an outer wall 116 of the nozzle member 111. Therefore, the chemical solution can be mixed more homogeneously than when it is mixed by the mixing method using the conventional Venturi tube.